Extension Attempts to Read Non-JSON Files As JSON.

[demasu]

• Issue Type: Bug
• Extension Name: swagger-viewer
• Extension Version: 2.2.2
• OS Version: Darwin x64 18.6.0
• VSCode version: 1.36.1

{
    "messages": [],
    "activationTimes": {
        "startup": false,
        "codeLoadingTime": 368,
        "activateCallTime": 17,
        "activateResolvedTime": 135,
        "activationEvent": "onLanguage:plaintext"
    },
    "runtimeErrors": [
        {
            "name": "SyntaxError",
            "message": "\"///<redacted>/css/main.css\" is not a valid JSON Schema"
        }
    ]
}